Collision avoidance media access method for shared networks

ABSTRACT

A method includes scheduling a grid of sub-burst slots in a media access plan, each sub-burst slot having a shorter duration than a minimal transmission burst duration and representing an opportunity for the initiation of a data transmission by a network device. A network device includes a sub-burst slot scheduler and a sub-burst slot grid aligner. The sub-burst slot scheduler publicizes the sub-burst slot media access plan to the network devices. The sub-burst slot grid aligner aligns the sub-burst slot grid in the event of a transmission.

FIELD OF THE INVENTION

The present invention relates to data networks generally and to mediaaccess allocation in data networks in particular.

BACKGROUND OF THE INVENTION

There are many different types of data networks, of which Ethernet isperhaps the best known. Some data networks have resource reservationschemes. One such network is HomePNA (Home Phoneline Network Alliance)v3.0, which is designed to work over existing telephone lines to createa home/small office network. U.S. Pat. No. 7,408,949, issued Aug. 5,2008 and assigned to the common assignee of the present invention,describes generally how to extend the HomePNA v3.0 standard to operateover such a hybrid network of telephone and coax lines.

HPNA v.3 and other such resource reservation networks have a scheduler,described hereinbelow, to guarantee media resources to network devices,to prevent collision between multiple network devices using the sameline and to ensure quality of service. In coax networks, preventivecollision detection limits the dynamic range of the network devices,which may impose physical limitations on the size of the network, so itis preferable to use collision avoidance methods for media access incoax networks.

Reference is now made to FIG. 1, which depicts a prior art data network10, comprising at least two network devices 12 and 14, connected tocomputers. Network device 12 comprises a modem 16 which includes, amongother items, a carrier sensor 20 and a transceiver 24. Network device 14comprises a modem 18 which includes, among other items, a carrier sensor20, a scheduler 22 and a transceiver 24. Scheduler 22 creates and sendsto each device on network 10 a media access plan (MAP) at the beginningof each transmission cycle. Transceiver 24 either transmits, or bothtransmits and receives data transmissions over network 10.

An exemplary timing diagram 40 for an exemplary transmission cycle ofnetwork 10 (FIG. 1) is shown in FIG. 2, reference to which is now made.Timing diagram 40 shows a detailed schedule of future transmissionopportunities (TXOPs) that are made available to specific networkdevices in the upcoming transmission cycle at specific andnon-overlapping times. The start time and length of each scheduled TXOPin the upcoming transmission cycle, such as TXOPs 44, 48 and 50 shown inFIG. 2, as well as the network device to which each TXOP is assigned, isscheduled by scheduler 22 (FIG. 1) in the MAP for the upcomingtransmission cycle. The transmission cycle is then initiated, as shownin FIG. 2, with the publication of the MAP by scheduler 22 to thenetwork devices on network 10 (FIG. 1) during MAP publicationtransmission 30. For example, as shown in timing diagram 40 of FIG. 2,TXOP 44 is shown to be the first TXOP and may be assigned to device 1,TXOP 48 is shown to be the second TXOP and may be assigned to device 2,and TXOP 50 is shown to be the third TXOP and may be assigned to device3. As shown in timing diagram 40, the MAP for the representedtransmission cycle, also includes a scheduled registration TXOP 54during which new devices may ask to join network 10.

After publication of the MAP during MAP publication transmission 30,device transmissions may begin. Each device recognizes a particular TXOPthat has been assigned to it according to the MAP, and either utilizesthe TXOP or passes on it.

In timing diagram 40 shown in FIG. 2, it may be seen that device 1utilizes TXOP 44, as illustrated by hatched area 56 indicatingtransmission activity of device 1 during TXOP 44. However, if, as shown,devices 2 and 3 do not use TXOPs 48 and 50, these assigned portions ofbandwidth are wasted. Furthermore, if no new devices use registrationTXOP 54 for registering, the bandwidth of TXOP 54 is also wasted.

As can be seen, the prior art MAP wastes significant resources whenscheduled TXOPs for transmission and registration are not fullyutilized. Due to the predetermined sizes of the TXOPs, which, at aminimum, are required to be sufficiently large to accommodate at leastone data frame, the method suffers from inefficient bandwidthutilization and high per device overhead. Predetermined TXOP size percycle also means that adaptation of bandwidth change is slow andcomplex. Small TXOPs relative to transmission burst size may causeHead-Of-Line (HOL) Blocking. Scalability suffers as the network capacitydrops with increasing network size. For bi-directional protocols such asTCP and TFTP only low data rates may be achieved due to long round-triptime (RTT).

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is a schematic illustration of a prior art data network;

FIG. 2 is a timing diagram illustration for an exemplary transmissioncycle of the network shown in FIG. 1;

FIG. 3 is a schematic illustration of a data network, constructed andoperative in accordance with a preferred embodiment of the presentinvention;

FIG. 4 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary sub-burst slot media access plan (SBSMAP)constructed in accordance with a preferred embodiment of the presentinvention and operative in the network shown in FIG. 3;

FIG. 5 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary alternative SBSMAP featuring an alternative groupscheduling scheme;

FIG. 6 is a comparative timing diagram illustration of a repeated typegroup scheduling scheme and a rotated type group scheduling scheme;

FIG. 7 is an illustration of a tabular representation of an exemplarySBSMAP constructed and operative in accordance with a preferredembodiment of the present invention;

FIG. 8 is an illustration of an exemplary Group_Type table in whichparameters used to define the SBSMAP of FIG. 7 are catalogued;

FIG. 9 is an illustration of a tabular representation of an exemplaryalternative SBSMAP having explicit group separators;

FIG. 10 is a timing diagram illustration of an exemplary transmissioncycle for the SBSMAP of FIG. 9;

FIG. 11 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary alternative SBSMAP featuring data packetpriority-based media access opportunity allocation;

FIG. 12 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary alternative SBSMAP featuring need-responsive datapacket priority-based media access opportunity allocation;

FIG. 13 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary alternative SBSMAP featuring bandwidthrequirement-based media access opportunity allocation;

FIG. 14 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary alternative SBSMAP featuring media accessstarvation prevention;

FIG. 15 is a timing diagram illustration for an exemplary transmissioncycle for an exemplary alternative SBSMAP featuring bandwidthrequirement-based media access opportunity allocation like that providedby the SBSMAP of FIG. 13, and starvation prevention like that providedby the SBSMAP of FIG. 14;

FIG. 16 is an illustration of a tabular representation of an exemplarySBSMAP in accordance with which media access may be provided to networkflows in an advanced quality of service scheme;

FIGS. 17A and 17B are timing diagram illustrations for an exemplarytransmission cycle for an exemplary alternative SBSMAP featuring theimplementation of Next Map opportunities;

FIG. 18 is a timing diagram illustration for exemplary transmissioncycles for exemplary SBSMAPs implemented in a multi-tenant unit (MTU) ora multi-dwelling unit (MDU);

FIG. 19A is a timing diagram illustration for an exemplary transmissioncycle for a TCP protocol running on the network shown in FIG. 1; and

FIG. 19B is a timing diagram illustration for an exemplary transmissioncycle for an exemplary SBSMAP implemented for a TCP protocol.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures and components have notbeen described in detail so as not to obscure the present invention.

The present invention may extend media access methods usingcarrier-sensing and collision avoidance techniques to allow multiplenetwork devices to perform collision-free burst-like media access withinshared transmission opportunities (TXOPs). For example, the presentinvention may be used to extend the media access method of HomePNA (HomePhone Network Alliance) v3.0. It will be appreciated that for HomePNAand other media access methods in which collision detection is feasible,it may be preferable to use collision avoidance due to other benefitswhich it entails.

In order to extend media access methods using carrier-sensing andcollision avoidance techniques to allow multiple network devices toperform collision-free burst-like media access within shared TXOPs, thepresent invention may replace fixed-size, non-overlapping TXOPs with agrid of appreciably smaller time slots, which may each represent anopportunity for the initiation of a data transmission by a networkdevice. The appreciably smaller time slots may be sub-burst slots, i.e.,the time allotted to each slot may be shorter than a minimaltransmission burst duration. It will be appreciated that the principaladvantage provided by minimally sized time slots such as sub-burst slotsmay be that when a network device does not use its assigned time slottransmission opportunity, minimal time may be wasted before theopportunity to transmit is passed to the next device in the queue.

Reference is now made to FIG. 3, which depicts a collision avoiding datanetwork 100 constructed and operative in accordance with the presentinvention. Data network 100 may comprise at least two network devices102 and 104, connected to computers. Network device 102 may comprise amodem 106 which may include, among other items, a carrier sensor 110,which may be similar to prior art carrier sensors, a transceiver 114,which may be similar to prior art transceivers, and a sub-burst slot(SBS) grid aligner 116. Network device 104 may comprise a modem 108which may include, among other items, a carrier sensor 110, atransceiver 114, a SBS grid aligner 116 and a sub-burst slot scheduler112. Sub-burst slot scheduler 112 may create and send to each device onnetwork 100 a media access plan having sub-burst slots (SBSMAP) at thebeginning of each transmission cycle. SBS grid aligner 116 may realignthe sub-burst slot grid according to the SBSMAP advertised by scheduler112, in accordance with the occurrence of transmissions.

It will appreciated that the configuration shown in FIG. 3 for network100 is exemplary, and that devices 102 and 104 which are illustrated inFIG. 3 as stand-alone devices, may operate as stand-alone devices or asintegrated components in other devices. For example, in alternativeconfigurations of network 100 constructed and operative in accordancewith a preferred embodiment of the present invention, either or both ofdevices 102 and 104 may be integrated into a personal computer, aset-top box, a television, a PVR or other device.

Like the prior art MAP, the SBSMAP provided by the present invention maydescribe a schedule of transmission opportunities (TXOPs) to each deviceon network 100. However, unlike the prior art MAP, the SBSMAP providedby the present invention may not exclusively reserve super-burst sizedportions of the TXOP for particular network devices or data flows.Rather, each scheduled sub-burst slot may constitute an opportunity ofbrief duration for the device or data flow with which it is associatedto begin transmitting. Each sub-burst slot may be much shorter in lengththan the predetermined, super-burst sized TXOPs of the prior art MAP.

It will be appreciated that the method for media access provided by thepresent invention may waste less bandwidth than the prior art due to thebrief duration of the sub-burst slots provided by the present invention,which if not used for initiating a transmission, may comprise a muchsmaller amount of wasted bandwidth than unused prior art TXOPs.

Reference is now made to FIG. 4 which shows an exemplary timing diagram200 for an exemplary transmission cycle of network 100 (FIG. 3). Asshown in FIG. 4, the transmission cycle is initiated with thepublication of the SBSMAP by SBS scheduler 112 to the network devices onnetwork 100 (FIG. 3) during SBSMAP publication transmission 230. Asshown in FIG. 4, a multiplicity of sub-burst slots SBS_(n) are scheduledin shared TXOP 205 in accordance with the SBSMAP. In accordance with apreferred embodiment of the present invention, each sub-burst slotSBS_(n) may represent an opportunity for the network device or data flowassociated with that sub-burst slot to initiate a transmission.Collectively, the sub-burst slots scheduled in accordance with theSBSMAP may form a grid of transmission opportunity start times. In theexample shown in FIG. 4, sub-burst slots SBS₁-SBS₂₃ form a grid oftransmission opportunity start times, initialized at the beginning ofshared TXOP 205.

In accordance with a preferred embodiment of the present invention, eachsub-burst slot SBS_(n) in the grid may serve as a placeholder, reservingthe opportunity for its associated network device or data flow totransmit at the time which the sub-burst slot occupies in the sequenceof sub-burst slots in the grid. For example, as shown in FIG. 4, thefirst opportunity to transmit is reserved for the network device or dataflow associated with SBS₁. The network device or data flow associatedwith SBS₁ may act on this opportunity to transmit, or pass on it.

In order for a network device to act on an opportunity to transmit, itmust initiate its transmission at the beginning of its associatedsub-burst slot. The duration of sub-burst slots in accordance with apreferred embodiment of the present invention may be 8-32 μsec and thewindow for acting upon the opportunity to initiate a transmission may bethe first 2-4 μsecs of the sub-burst slot. It will be appreciated thatthe duration of each sub-burst slot in accordance with a preferredembodiment of the present invention may be a variable parameter, whichmay be varied in a fixed scheme or a dynamic scheme. For example,sub-burst slot duration may be varied according to the characteristicsof the devices which may participate in the network.

In the event that the transmission opportunity provided by a sub-burstslot SBS_(n) is not utilized by the network device or data flowassociated with it, the network device or data flow associated with thenext sub-burst slot SBS_((n+1)) in the grid sequence may then be giventhe opportunity to transmit.

Returning now to FIG. 4, it may be seen in the illustrated example thatno transmissions occur during shared TXOP 205 until the fourthtransmission opportunity allotted to network device DEV-1, which isassociated with the sub-burst slot numbered “0” in the figure. As shownin transmission activity diagram 212 for network device DEV-1, networkdevice DEV-1 passes on the transmission opportunities presented by thesub-burst slots SBS₁, SBS₅ and SBS₉ numbered “0”, and transmits for thefirst time during sub-burst slot SBS₁₃. During SBS₁₃ network deviceDEV-1 begins transmitting, and occupies the transmission medium untilits transmission is complete. It will be appreciated, therefore, asillustrated in FIG. 4, that when utilized for a transmission, thesub-burst slots provided by the present invention may be expandable,expanding to allow the completion of the transmission begun by thenetwork device during the sub-burst slot. The lengths to which thesub-burst slots may expand may be unlimited, or they may be limited. Theend of a shared TXOP may constitute a limit to the expansion of asub-burst slot during a transmission. Alternatively, a transmission mayextend the length of a shared TXOP.

As described hereinabove, at the beginning of each cycle, the networkdevices on network 100 may receive a schedule of transmissionopportunities, i.e. an SBSMAP detailing a lineup of sub-burst slots.Transmissions may then occur, such as the exemplary transmissions shownin FIG. 4 during sub-burst slots SBS₁₃, SBS₁₇ and SBS₂₃. The end of atransmission may be identified by an Inter Frame Gap (IFG) 202, such asthose shown in FIG. 4 succeeding the transmissions during sub-burstslots SBS₁₃ and SBS₁₇.

When transmissions occur, SBS grid aligner 116 (FIG. 3) in each networkdevice on network 100 may recalculate the timing of the sub-burst slotgrid so that each network device may know at what time its nexttransmission opportunity is scheduled. While the order of the sub-burstslots in the grid is known because that information is provided to eachnetwork device in the advertised SBSMAP, the timing of the grid ischanged due to, and in direct accordance with, the duration of thetransmissions which occur.

It may further be seen in FIG. 4 that while the sub-burst slots numbered“0” are associated with network device DEV-1, the sub-burst slotsnumbered “1” are associated with network device DEV-2, and the sub-burstslots numbered “3” are associated with the network device DEV-4. Thismay be seen in the transmission activity diagrams 214 and 216, whichshow transmission activity for network devices DEV-2 and DEV-4respectively. It is shown that after passing on its first 5 transmissionopportunities provided by sub-burst slots SBS₂, SBS₆, SBS₁₀, SBS₁₅ andSBS₁₉ numbered “1”, network device DEV-2 transmits during SBS₂₃. It isalso shown that network device DEV-4 passes on its first threetransmission opportunities (SBS₄, SBS₈ and SBS₁₂) and then transmitsduring SBS₁₇.

In the example shown in FIG. 4 each network device numbered N isassociated with the sub-burst slots numbered N−1. It may therefore alsobe understood from FIG. 4 that the sub-burst slots numbered “2” areassociated with network device DEV-3 which does not transmit at allduring TXOP 205. However, it will be appreciated that in accordance witha preferred embodiment of the present invention, a particular sub-burstslot may be associated with any network device or data flow, and thatthe identity of the network device or data flow associated with aparticular sub-burst slot may be encoded in the SBSMAP, as will beexplained later in further detail with respect to FIG. 7.

In accordance with an additional preferred embodiment of the presentinvention, sub-burst slots may be organized in modular groups, and thesemodular group units may be assembled into group sequences of one or moregroups and scheduled in the SBSMAP. A group may consist of a particularsequence of sub-burst slots, each of which is associated with aparticular network device or data flow. Each group may also beassociated with a particular one of a plurality of group types. Inaccordance with a preferred embodiment of the present invention, grouptypes may dictate scheduling protocol in various instances. For example,in the event of the interruption of a group sequence by a transmission,SBS scheduler 112 (FIG. 3) may determine which sub-burst slot may bescheduled after the transmission in accordance with the group type ofthe interrupted group. Scheduling schemes for the repetition, rotationor omission of a group or sequence of groups in a TXOP may also bedictated by group type.

Group affiliation, i.e., which sub-burst slots comprise a group of whichtype, in addition to network device and data flow association, may alsobe encoded in the SBSMAP, in accordance with a preferred embodiment ofthe present invention, as will be discussed later in further detail withrespect to FIG. 7.

In the example shown in FIG. 4, TXOP 205 is scheduled with successiverepetitions of group Fx, a fixed type group comprising the sequence ofsub-burst slots “0,1,2,3”, where each sub-burst slot is associated witha network device according to the formula N+1, where N is the number ofthe sub-burst slot. As shown in FIG. 4, the scheduling scheme dictatedby a fixed group, in accordance with a preferred embodiment of thepresent invention, is that a transmission constitutes an interruption ofthe continuity of the current group sequence, and that after thetransmission, the scheduled lineup begins with the first sub-burst slotin the group. This may be seen in FIG. 4 when the transmission duringSBS₁₃ interrupts the fourth repetition of group Fx, Fx₄, and the fifthrepetition of group Fx, Fx₅, beginning with sub-burst slot “0”, isscheduled after the transmission.

An alternative scheduling scheme, as dictated by a different group type,is shown in FIG. 5, reference to which is now made. FIG. 5 shows timingdiagram 300 for an exemplary SBSMAP constructed and operative inaccordance with a preferred embodiment of the present invention, similarto timing diagram 200 shown in FIG. 4. Similar elements in FIGS. 4 and 5are referred to by corresponding reference numerals.

In FIG. 5, the basic modular group unit R, of which successiverepetitions are scheduled in shared TXOP 305, comprises a sequence ofsub-burst slots “0,1,2,3”, which is identical to the sequence ofsub-burst slots of group Fx in FIG. 4. However, because they areassociated with different group types, group Fx and group R dictatedifferent scheduling schemes in shared TXOPs 205 and 305 respectively.

In the example shown in FIG. 5, three scheduled rounds of group R, R₁,R₂ and R₃ pass with no transmissions occurring. During sub-burst slotSBS₁₃ numbered “0” in group R₄, network device DEV-1 transmits. As shownin FIG. 5, the scheduling protocol associated with group R dictates thatafter a transmission, the group sequence continues uninterrupted. Thus,the next sub-burst slot scheduled, SBS₁₄ is shown to be numbered “1”. Itmay further be seen in FIG. 5 that the remainder of group R4, andsimilarly, group R5, are scheduled fully without regard for‘interruptions’ caused by transmissions.

Reference is now made to FIG. 6 which illustrates two additionalexemplary group types provided in accordance with a preferred embodimentof the present invention, the repeated group type (R0) and the rotatedgroup type (R1). In accordance with a preferred embodiment of thepresent invention, both the rotated and repeated group types share thepost-transmission scheduling characteristics of group R, describedhereinabove with respect to FIG. 5. That is, after a transmission, thescheduling of the group sequence continues uninterrupted, unlike in thecase of fixed groups, described hereinabove with respect to FIG. 4.However, the rotated and repeated groups dictate different schemes forthe continued scheduling of a group or sequence of groups in a TXOP.

FIG. 6 shows two exemplary timing diagrams 600 and 620. It may be seenin timing diagram 600 that the schedule of groups scheduled by an SBSMAPfor TXOP 605 comprises the initial modular sequence 602 of the groups“Fx0, R0, R1”, where group Fx0 comprises the sequence of sub-burst slots“0,1,2”, group R0 comprises the sequence of sub-burst slots “0,1,2,3”,and group R1 comprises the sequence of sub-burst slots “0,1,2,3,4”. Inaccordance with a preferred embodiment of the present invention, thetype of the last group in initial modular sequence 602 may determinewhich group or groups may be scheduled for the remainder of the durationof the TXOP. For example, as shown in FIG. 6, the last group in initialmodular sequence 602 is R1, a rotated type group. Accordingly, as perthe TXOP remainder scheduling scheme associated with the rotated grouptype, the sequence of groups in initial modular sequence 602, i.e. “Fx0,R0, R1”, is rescheduled in REP1 in TXOP 605, as shown in FIG. 6.

In timing diagram 620, the constituent groups of initial modularsequence 622 are the groups “Fx0, R1, R0”, such that the only differencebetween initial modular sequence 602 and initial modular sequence 622 isthe alternative positions of groups R1 and R0 in the two sequences. Morespecifically, the difference between the two sequences is that the lastgroup in initial modular sequence 602 is rotated group R1, and the lastgroup in initial modular sequence 622 is repeated group R0. It is shownin FIG. 6 that the TXOP remainder scheduling scheme which may beassociated with the repeated type group is the continued repetition ofthe last group in the initial modular sequence of the SBSMAP. It isaccordingly shown in FIG. 6 that repeated group R0 is repeated in Rep1,Rep2 and for the remainder of TXOP 625.

It will be appreciated that the group type dependent scheduling schemesand protocols provided by the present invention may not be limited tothe exemplary scheduling schemes and protocols described hereinabovewith respect to FIGS. 4, 5 and 6. For example, an additionalpost-transmission scheduling protocol which may be incorporated into anSBSMAP provided by the present invention may be an alternative fixedscheme, which may be associated with the alternative fixed group type.The post-transmission scheduling protocol dictated by the alternativefixed group may be similar to the fixed group scheme described withrespect to FIG. 4. However, after a transmission, the first sub-burstslot to be scheduled may not be the first-sub-burst slot in the group.The alternative fixed group type may dictate that the assignment of thefirst sub-burst slot to be scheduled after a transmission may rotatethrough the group sub-burst slots in a round-robin manner.

Additional TXOP remainder scheduling schemes may include, for example,alternative repeated schemes in which a selection of the groups in theinitial modular sequence, rather than just the final group in thesequence may be repeated for the remainder of the TXOP. For example, thegroup type “repeated_final_2” may dictate the repetition of the last twogroups in the initial modular sequence for the remainder of the TXOP. Agroup type “initial” may dictate that the group or groups associatedwith the group type “initial” in the initial modular sequence may onlybe scheduled once in a TXOP, overriding the scheduling instructions ofother scheduling schemes pertaining to that group or groups, which mightotherwise dictate that it or they be rescheduled.

It will be appreciated that the creation of an SBSMAP using groups asmodular building blocks whose constituent participants may be chosen forparticular effect, and which may be scheduled in the SBSMAP in schemesdesigned for particular effect may provide a highly flexible andcustomizable bandwidth allocation method. A significant measure ofcontrol over the allocation of transmission opportunities to particularnetwork devices and data flows may thus be provided by the presentinvention.

Reference is now made to FIG. 7 which shows how the scheduling schemesand protocols described hereinabove may be encoded into an SBSMAPconstructed and operative in accordance with a preferred embodiment ofthe present invention and represented in tabular form. As shown in table363 in FIG. 7, the parameters which may be used to define an SBSMAP inaccordance with a preferred embodiment of the present invention may beRow_Number 350, Device_ID 352, Group_Type 354, Flow_ID 356, Length 358and TXOP_Number 360. Row_Number 350 may be a sequential serial numberassigned to each row in the SBSMAP table. Device_ID 352 may be anidentification number corresponding to a particular network device.Group_Type 354 may be an identification number associated with aparticular group type. Flow_ID 356 may be an identification numberassociated with a data flow. Length 358 may be the duration allocated toa TXOP, and TXOP_Number 360 may be a sequential serial number assignedto each sequential TXOP.

In table 363, which is an example of an implicit SBSMAP table, each row365 in the table may correspond to a sub-burst slot in the SBSMAP. Thismay not be the case in an explicit SBSMAP table which will be explainedlater with respect to FIG. 9.

In accordance with a preferred embodiment of the present invention, theassociation of a sub-burst slot with a particular network device anddata flow as well as its group affiliation may be encoded in the SBSMAPtable, as shown in FIG. 7. The association of a sub-burst slot with aparticular network participant may be defined by the parametersDevice_ID 352 and Flow_ID 356. A sub-burst slot may thereby beassociated with a particular network device, a particular group ofnetwork devices, a particular data flow or group of data flows, or aparticular data flow or group of data flows restricted to a particularnetwork device or group of network devices.

In accordance with a preferred embodiment of the present invention,certain values of Device_ID 352 and Flow_ID 356 may be reserved forinternal network control and assignment definition. For example, aDevice_ID value of 0 may be reserved for the group of all the networkdevices, including unregistered devices, while Device_ID values of 1-62may be reserved for particular network devices or groups of devices. Forany Device_ID 1-62, a Flow_ID of 0 may be reserved for network controlflows while the Flow_ID values 1-63 may be reserved for particularflows. The Device_ID value of 63 may be reserved for assignmentdefinition. In conjunction with a Device_ID of 63, particular Flow_IDvalues may be reserved to trigger particular scheduling schemes, as willbe discussed later in further detail with respect to FIGS. 14-17B.

Group affiliation, i.e., which sub-burst slots comprise a group of whichtype may be encoded in the SBSMAP via particular value assignments inGroup_Type parameter 354. Each group type may be associated with aparticular Group_Type value. For example, the Group_Type value “4” maybe associated with the group type “fixed”, the Group_Type value “5” maybe associated with the group type “rotated” and the Group_Type value “6”may be associated with the group type “repeated”.

In the example shown in FIG. 7, it is shown that the SBSMAP defined bytable 363 has two TXOPs T0 and T1. The first TXOP T0 has a duration ofL₀, in which one group, group j, which is a fixed type group, isscheduled. It may also be seen that group j comprises one sub-burstslot, and since this sub-burst slot is the sole sub-burst slot in TXOPT0, its duration is also L₀.

The second TXOP in the SBSMAP defined by table 363 is T1, having alength L₁. In accordance with a preferred embodiment of the presentinvention, initial modular sequence 369 is scheduled for the duration L₁in accordance with the scheduling schemes dictated by the SBSMAPparameters. It is shown in FIG. 7 that initial modular sequence 369comprises group k, a rotated type group having two sub-burst slots,followed by group l, a repeated type group having four sub-burst slots.It may therefore be understood that after the first scheduling ofinitial modular sequence 369 in TXOP T1, group l will repeat for theduration of the TXOP length L₁.

The SBSMAP provided by the present invention may also include aregistration sub-burst slot during which new devices may request to beadded to network 100. In the example shown in FIG. 7 it may be seen thatthe sub-burst slot in group j is a registration sub-burst slot, sinceits Device_ID is 0 and its Flow_ID is 63. In the example shown in FIG. 7the exemplary Device_ID value of “0” indicates “all devices”, includingunregistered ones, and the exemplary Flow_ID value of 63 indicates aregistration sub-burst slot.

As provided by the present invention, access to registration sub-burstslots may be contention-based, and collisions may occur. A higher levelprotocol may handle retries.

It will be appreciated that network bandwidth overhead may beappreciably reduced by the replacement of a long registration TXOP witha shorter registration time-slot, such as a sub-burst slot, which maymonopolize a minimum of bandwidth in the event that it is not used.

FIG. 8, reference to which is now made, shows an exemplary Group_Typetable 370 in which the group types provided by the present invention maybe catalogued. In Group_Type table 370 additional descriptive parametersare listed alongside Group_Type values 354. The parameters provided intable 370 for each Group_Type value, as shown in table 370, areTX_Policy 372, Group_Scheme 374 and Description 376.

It may be seen in FIG. 8 that the TX policy of group type “0” is “state”while the TX policy of group types “4”, “5” and “6” is “edge”. A “state”TX policy indicates that the transmission opportunity having this TXpolicy is a prior art TXOP during which transmission of data by thenetwork device associated with that TXOP may occur at any time duringthe TXOP. In contrast, an “edge” TX policy indicates that thetransmission opportunity having this TX policy is a sub-burst slotprovided by the present invention, during which transmission of data bythe network device associated with the sub-burst slot must occur duringthe initial few μsecs of the sub-burst slot. The term “collisiondetection (CD) method” included in the description of group type “0”compared with the term “sub-burst (SB) slot method” included in thedescription of group types “4”, “5” and “6” further conveys that thetransmission opportunities associated with a Group_Type of “0” areprior-art TXOPs, while the transmission opportunities associated withgroup types “4”, “5” and “6” are sub-burst slots provided by the presentinvention.

It will be appreciated that prior-art group type “0” is not irrelevantto table 370, as might be expected, due to the association of this grouptype with the prior-art, and the association of table 370 with thepresent invention, i.e. SBSMAPS comprising groups of sub-burst slots. Itwill therefore be appreciated that prior-art group type “0” is includedin table 370 because an SBSMAP provided by the present invention mayinclude prior-art TXOPs alongside inventive TXOPs containing sub-burstslots.

Reference is now made to FIG. 9 which shows an explicit SBSMAP table470, defining an SBSMAP constructed and operative in accordance with anadditional preferred embodiment of the present invention. In exemplaryexplicit SBSMAP table 470, each row may not correspond to a scheduledsub-burst slot. An additional row, operating as an explicit groupseparator, may be included in the table after a row pertaining to thefinal group member of a group, in order to define a duration allotted tothat group which may be shorter than the combined duration of all of thesub-burst slots in the group. This shorter duration may only besufficient for scheduling sub-burst slots for a portion of the membersof the group, rather than for all of them. Alternatively, the durationallotted to a group by an explicit group separator may be longer thanthe combined duration of all of the sub-burst slots in the group.

In the example shown in FIG. 9, a Device_ID value of 63 and a Flow_IDvalue of 63 identify rows 472, 473, 474 and 475 as explicit groupseparator rows. Accordingly, as shown in table 470, group j isexplicitly allotted a bandwidth duration of D0, rather than the defaultcumulative duration of all of its group member sub-burst slot durations.Similarly, in TXOP T1, the first scheduling of group k, k₁, isexplicitly allotted a bandwidth duration of D1, group m is explicitlyallotted a bandwidth duration of D2 and the second scheduling of groupk, k₂, is explicitly allotted a bandwidth duration of D3.

Reference is now made to FIG. 10 which shows timing diagram illustration650 for an exemplary transmission cycle for the SBSMAP shown in FIG. 9.Diagrams Dj, Dk and Dm in FIG. 10 clarify sub-burst slot affiliationwith groups j, k and m.

Exemplary timing diagram 650 shows two repetitions of each of the twoTXOPs T0 and T1 scheduled in SBSMAP 470 in FIG. 9, such that the fourTXOPs shown in timing diagram 650 are T0 ₁, T1 ₁, T0 ₂ and T1 ₂.

In the two schedulings of group j shown in timing diagram 650, j-T0 ₁and j-T0 ₂, which are scheduled in TXOPs T0 ₁ and T0 ₂ respectively, itmay be seen that duration D0 allotted to the scheduling of group j issufficient to allow the scheduling of three out of the four groupmembers of group j. As shown in timing diagram 650, the first threesub-burst slots in group j, numbered “0”, “1” and “2” are scheduledaccordingly in the first scheduling of group j, j-T0 ₁. In the secondscheduling of group j, j-T0 ₂, it may be seen that the schedulingsequence begins at the point where the scheduling in j-T0 ₁ ended, withthe fourth and final group member, associated with the sub-burst slotnumbered “3” in group j. Once a full round of the sequence is complete,after the first sub-burst slot scheduled in j-T0 ₂, the sequence isrestarted, as shown by the scheduling of sub-burst slot “0” in thesecond sub-burst slot position in j-T0 ₂. The orderly, rotationalprocession through the sequence of group members from first to last,then returning to the first to begin again is illustrated in diagram Dj,where the overall sequence of sub-burst slots scheduled for group j inj-T0 ₁ and j-T0 ₂ may be seen to be “0,1,2,3,0,1”.

With respect to durations D1 and D3 assigned to the first and secondschedulings respectively of group k in TXOP T1, and duration D2 assignedto the scheduling of group m in TXOP T1, as shown in table 470 (FIG. 9),it may be seen in the corresponding timing diagram 650 in FIG. 10 thatdurations D1 and D3 are each sufficient to allow the scheduling of threeout of the five group members of group k, and that duration D2 issufficient to allow the scheduling of four out of the six group membersof group m. The orderly rotational scheduling of the group k and mmembers, like that of the group j members, is shown in diagrams Dk andDm respectively. It may be seen in diagram Dk that the overall sequenceof sub-burst slots scheduled for group k in k₁-T1 ₁, k₂-T1 ₁, k₁-T1 ₂and k₂-T1 ₂ is “0,1,2,3,4,0,1,2,3,4,0,1”. In diagram Dm it may be seenthat the overall sequence of sub-burst slots scheduled for group m inm-T1 ₁ and m-T1 ₂ is “0,1,2,3,4,5,0,1”.

It will be appreciated that sub-burst slots in different groupsidentified by the same numeral in timing diagram 650, i.e. the sub-burstslots numbered “2” in groups j and m, may not be associated with thesame network participant. A numeral identifying a sub-burst slot intiming diagram 650 may correspond to the position of the sub-burst slotin its group sequence, while the network participant with which thesub-burst slot is associated is the network participant associated withthe Device_ID and Flow_ID values associated with that sub-burst slot, aslisted in corresponding SBSMAP table 470 (FIG. 9). For example, thesub-burst slot numbered “1” in group m is the second sub-burst slot inthe group sequence, after the sub-burst slot numbered “0” and before thesub-burst slot numbered “2”. In SBSMAP table 470 in FIG. 9, the secondsub-burst slot in group m is seen to be the sub-burst slot associatedwith row 13 in table 470. The network participant associated with thesub-burst slot numbered “1” in group m is therefore the networkparticipant associated with Device_ID “1” and Flow_ID “1” as listed inrow 13 of table 470.

Reference is now made to FIG. 11 in which timing diagram 700 is shownfor an exemplary transmission cycle for an SBSMAP constructed andoperative in accordance with an additional preferred embodiment of thepresent invention. In this embodiment media access may be allocated tonetwork devices according to the priority of the data packets which willbe transmitted by the devices. Accordingly, high priority transmissionsmay be provided the first media access opportunities, and lower prioritytransmissions may only subsequently be provided media accessopportunities. Any number of priority levels may be used. For example,the eight IEEE 802.1P priority levels may be mapped to fewer than eightmedia access priorities, e.g. three levels including high (H), medium(M) and low (L). It will also be appreciated that these eight prioritylevels, or another group of priority levels, may be mapped to adifferent group of priority levels according to any suitable scheme.

It may be seen in FIG. 11 that successive repetitions of the groupcomprising the sequence of sub-burst slots “0, 1, 2, 3” are scheduled inshared TXOP 705. In accordance with this embodiment of the presentinvention, and as shown in FIG. 11, each group scheduled in TXOP 705 isassociated with a priority level, allowing the transmission only of datapackets having a priority level equal to or exceeding this level duringthe sub-burst slot opportunities in the group. For example, as shown inFIG. 11, the sub-burst slot opportunities in scheduled groups H1, H2, H3and H4 are associated with a high priority level H, and may only be usedfor the transmission of high-priority data packets. The sub-burst slotopportunities in scheduled groups M1 and M2 are associated with a mediumpriority level M, and may be used for the transmission of data packetsof medium or higher priorities. The sub-burst slots opportunities inscheduled group L1 are associated with a low priority level L, and maybe used for the transmission of data packets of any priority.

It will be appreciated that in accordance with this embodiment of thepresent invention, the order of priority-affiliated groups scheduled inthe SBSMAP descends from higher priority to lower priority. This isshown in FIG. 11 where the first three groups scheduled in TXOP 705 arethe high priority group H₁, the medium priority group M₁ and the lowpriority group L₁, in that order. It may further be seen that after oneof each group has been scheduled, i.e. after the scheduling of group L₁,the scheduling sequence returns to the first group in the sequence ofgroups, i.e. the high priority group H, and thus group H₂ is seen to bescheduled in the position of the fourth scheduled group.

The precedential location of higher priority groups in the sequence ofgroups in the SBSMAP, ensures quantitatively preferential schedulingstatus to the higher priority groups due to the post-transmissionscheduling scheme provided in this embodiment, which, after atransmission, returns the opportunity to transmit to the first group inthe sequence of groups. As shown in FIG. 11, after the transmissionduring sub-burst slot “0” in group H₂, high-priority group H₃ isscheduled, rather than a medium-priority group. Again after thetransmission during sub-burst slot “0” in group H₃, high-priority groupH₄ is scheduled, rather than a medium-priority group. As shown in FIG.11, the result of precedential location of the high-priority groups inthe sequence of groups in the SBSMAP results in repeated scheduling ofthe higher priority groups at the expense of the lower priority groups.

In an additional preferred embodiment of the present invention, mediaaccess may be allocated according to a more efficient priority-basedscheme than that provided in the embodiment described with respect toFIG. 11. This embodiment is illustrated with respect to FIG. 12,reference to which is now made, in which timing diagram 750 is shown foran exemplary transmission cycle for an SBSMAP constructed and operativein accordance with an additional preferred embodiment of the presentinvention.

In this embodiment, scheduler 112 (FIG. 3) may schedule sub-burst slotsassociated with a particular priority level to network devices whichinform scheduler 112 that they have data packets of that priority levelto transmit. Network devices which do not inform scheduler 112 ofparticular priority needs may be assigned low priority sub-burst slotsby scheduler 112 by default. Media access opportunities may thus be moreprecisely reserved for allocation where they are needed, and not wastedwhere they are not needed.

In order to allocate sub-burst slot transmission opportunities inaccordance with data packet priorities to be transmitted by devices, asshown in FIG. 12, scheduler 112 (FIG. 3) may allocate sub-burst slottransmission opportunities for each device in all of the groupsassociated with a priority level equal to or below the priority levelrequested by each device. In the example shown in FIG. 12, it may beseen that the network devices associated with sub-burst slots “0” and“1” informed scheduler 112 that they have high priority data packets totransmit. Accordingly, sub-burst slots numbered “0” and “1” are seen tobe scheduled in the groups of every priority, i.e. “H”, “H,M” and“H,M,L”. It may further be seen that the network device associated withsub-burst slot “2” informed scheduler 112 that it has medium prioritydata packets to transmit. Accordingly, sub-burst slots numbered “2” areseen to be scheduled in the groups having medium and lower priorities,i.e. “H,M” and “H, M, L”. Network devices not informing scheduler 112that they have medium or high priority data packets to transmit, such asthose associated with sub-burst slots “3” and “4”, as may be seen inFIG. 12, are scheduled in the low priority group “H,M,L” only.

It will be appreciated that in this more efficient priority-basedscheme, sub-burst slot opportunities are not wasted on higher priorityopportunities for devices that do not have higher priority data packetsto transmit. The streamlined result, in which the quantity of members ofa group increase with decreasing priority of the group may be seen inFIG. 12, where the highest priority group “H” has two members, the nexthighest priority group “H,M” has three members, and the lowest prioritygroup “H,M,L” has five members.

It will also be appreciated that in this embodiment of the presentinvention, high priority groups may enjoy the same quantitativelypreferential scheduling as described previously with respect to FIG. 11,owing to the precession of the high priority groups in the sequence ofgroups in the SBSMAP and the post-transmission scheme of returning tothe first group in the sequence of groups after a transmission. As inFIG. 11, the initial order of groups in the SBSMAP in FIG. 12 is shownto descend from the highest priority group to the lowest priority group,as shown in the scheduling of groups H₁, M₁ and L₁, in that order, inTXOP 755 in FIG. 12. Furthermore, as in FIG. 11, the post-transmissionreturn to the scheduling of the first group in the sequence of groups,i.e. the highest priority group, is shown in FIG. 12, where after thetransmission during sub-burst slot “0” in group H₂, high-priority groupH₃ is scheduled, rather than a medium-priority group. As in FIG. 11, theresult is repeated scheduling of the higher priority groups at theexpense of the lower priority groups.

An additional preferred embodiment of the present invention is shown inFIG. 13, reference to which is now made. In this embodiment,transmission opportunities may be allotted non-equally to group members,in accordance with the bandwidth requirements of the networkparticipants associated with the members of the group. In this method,sub-burst slot grid scheduler 112 (FIG. 3) may allocate a quantity ofsub-burst slot opportunities to each participant which is proportionateto the bandwidth requirements of each participant.

An exemplary non-equal allotment of transmission opportunities tonetwork participants in a group is shown in exemplary timing diagram 800for an exemplary transmission cycle for an SBSMAP constructed andoperative in accordance with this embodiment of the present invention. Aseries of groups g are shown to be scheduled in timing diagram 800. Eachgroup g comprises the sequence of sub-burst slots “0,1,2,3,4,5”. Asshown in rows 810, 812 and 819 corresponding to network participants 1(Dev-1), 2 (Dev-2) and 3 (Dev-3) respectively, it may be seen that foreach group g, sub-burst slots “0”, “2” and “4” are associated withnetwork participant 1, sub-burst slots “1” and “3” are associated withnetwork participant 2, and sub-burst slot “5” is associated with networkparticipant 3.

As shown in FIG. 13, preference for the allotment of transmissionopportunities may be conferred upon particular network participants atthe expense other network participants, reflecting varying amounts ofbandwidth requested by the network participants according to theirneeds. In the example of group g, as shown in FIG. 13, the relativeproportions of bandwidth requested by network participants 1, 2 and 3are shown to be 3:2:1 respectively. Network participant 1 is shown to beallotted one half of the transmission opportunities, network device 2 isshown to be allotted two sixths of the transmission opportunities, andnetwork device 3 is shown to be allotted one sixth of the transmissionopportunities.

An additional preferred embodiment of the present invention is shown inFIG. 14, reference to which is now made. In accordance with theembodiment of the present invention illustrated in FIG. 14, an SBSMAPconstructed and operative in accordance with a preferred embodiment ofthe present invention may include a mechanism for “starvationprevention”. Network participants may starve for lack of transmissionopportunity if, for example, they belong to a group having a lowpriority for the allotment of transmission opportunities, and othergroups having a higher priority for the allotment of transmissionopportunities are feasting on those opportunities and generally hoggingthe communal TXOP. The starvation prevention mechanism provided by thepresent invention and described with respect to FIG. 14 may preventnetwork participant starvation by occasionally throwing a bone, i.e. atransmission opportunity, to the disadvantaged group. This “wild card”transmission opportunity may be rotated through the disadvantaged groupso that the participants in the disadvantaged group may receivetransmission opportunities on a round robin basis.

It may be seen in exemplary timing diagram 830 in FIG. 14 that groups jand k are scheduled in TXOP 835 according to an SBSMAP associated withtiming diagram 830. It may also be seen that the network participantsassociated with sub-burst slots “0”, “1”, “2” and “3” in group k aredisadvantaged in comparison with the network participants associatedwith sub-burst slots “0” and “1” in group j, since group j is scheduledfive times in TXOP 835 and group k is scheduled only twice. In timingdiagram 830 it may be seen that the reason for this inequality is theprecession of group j with respect to group k in the SBSMAP, and, as thefirst group in the sequence of groups “j, k” in the SBSMAP, schedulingrestarts with group j after each transmission. This may be seen intiming diagram 830 where after the transmission in group j₂, group j₃ isscheduled, and after the transmission in group j₃, group j₄ isscheduled, and after the transmission in group j₄, group j₅ isscheduled. Consequently, as may be seen in FIG. 14, the networkparticipants associated with sub-burst slots “0”, “1”, “2” and “3” ingroup k are starved for transmission opportunities due to the nearmonopolization of TXOP 835 by group j.

To provide a measure of correction for this type of inequitabledistribution of transmission opportunities, Next_Group opportunities maybe scheduled by scheduler 112 (FIG. 3) in an SBSMAP constructed andoperative in accordance with a preferred embodiment of the presentinvention. In the example shown in FIG. 14, a Next_Group opportunity “N”is shown to be scheduled into group j after the group j sequence “0,1”.As shown in diagram 839 pertaining to group k, the Next_Groupopportunity serves as an additional sub-burst slot which is assigned tothe next participant in the queue in group k. This is illustrated indiagram 839 in which the group k sub-burst slot transmissionopportunities are seen to be numbered in the repeating consecutivesequence “0,1,2,3,0,1,2,3,0,1”, wherein the first, sixth, seventh andeighth sub-burst slot transmission opportunities are Next_Groupopportunities contributed to group k by group j. Group k is thereby lessstarved of transmission opportunities owing to the transmissionopportunities bequeathed to it by group j via the Next_Groupopportunities scheme.

In an additional preferred embodiment of the present invention shown inFIG. 15, reference to which is now made, a more deliberateimplementation of the Next_Group opportunity may not provide merely ameasure of correction for an inequitable distribution of transmissionopportunities, but may calculatingly correct the distribution oftransmission opportunities among the network participants so that notonly the participants in the first group scheduled in the SBSMAP may beguaranteed the bandwidth they require, but also the participants in thesucceeding groups may be guaranteed the bandwidth they require.

As shown in FIG. 15, an amount of bandwidth B may be allotted to thefirst group scheduled in the SBSMAP. In exemplary timing diagram 850, anamount of bandwidth B is shown to be allotted to group j₀, the firstscheduled group in the SBSMAP. Because there are four sub-burst slots ingroup j, bandwidth B may be divided into quarters, with each sub-burstslot allotted one quarter of bandwidth B. Each network flow associatedwith each of sub-burst slots “0”, “1” and “2” in group j₀ may thereby beassured a minimum bandwidth of B/4.

It will be appreciated, as shown in FIG. 15, that the fourth sub-burstslot in group j is a Next_Group opportunity. In the example shown inFIG. 15, Next_Group opportunity N₀ may bequeath at least one quarter ofbandwidth B, but as much as all of the remaining bandwidth not utilizedduring the duration of the group j₀ sub-burst slots, in the event thatone or more of the group j₀ transmission opportunities are not actedupon, to group k₀.

Diagram 860 in FIG. 15 illustrates the worst case scenario in which onlyone quarter of bandwidth B is guaranteed by Next_Group opportunity N₀ togroup k₀. The five participants in group k₀, further to a division ofthe bandwidth B/4 into five equal parts, are thereby each assured aminimum bandwidth of B/20. Two repetitions Rep0 and Rep1 of initialmodular sequence 852 of the SBSMAP, are shown to be scheduled in TXOP855 in accordance with the group type of group k₀, which is “rotated”.It may further be seen in FIG. 15 that additional repetitions of initialmodular sequence 852 are scheduled for the remaining duration of TXOP855 in accordance with the TXOP remainder scheduling scheme provided bythe present invention for rotated groups.

In an additional preferred embodiment of the present invention, shown inFIG. 16, reference to which is now made, media access may be provided tonetwork flows in an advanced quality of service scheme. In accordancewith the advanced quality of service scheme provided by the presentinvention, the network services may negotiate with scheduler 112 (FIG.3) for varying levels of guaranteed bandwidth. As shown in FIG. 16,which shows table 905, the tabular representation of the configurationof an SBSMAP constructed and operative in accordance with an additionalpreferred embodiment of the present invention, a service, like a networkparticipant, may be associated with a unique pair of values provided bythe Device_ID and Flow_ID values 352 and 356 respectively. In accordancewith this definition, it may be seen in FIG. 18 that sub-burst slots“1”, “8” and “12” are associated with a particular service having theDevice ID value of 1 and the Flow_ID value of 1. Similarly, it may beseen that sub-burst slots “2”, “4”, “6”, “9” and “13” are associatedwith a different service having the Device ID value of 2 and the Flow_IDvalue of 1. Sub-burst slots listed in SBSMAP table 905 as having thesame pair of values for the Device_ID and Flow_ID parameters may besimilarly associated with a service identified with that pair of values.

The groups into which the 17 sub-burst slots shown in SBSMAP table 905are grouped in the SBSMAP defined by SBSMAP table 905 are also encodedin the table data. As indicated by dashed line 912, group j comprisesthe first three sub-burst slots having a Group_Type value of 5, whichvalue may indicate a rotated group. As indicated by dashed line 914,group k comprises the next four sub-burst slots having a Group_Typevalue of 6, which value may indicate a repeated group. Similarly, dashedline 916 indicates that group l comprises the next four sub-burst slotswhich have a Group_Type value of 5, and group m closes out the groupsequence assigned to TXOP T0 with the next six sub-burst slots whichhave a Group_Type value of 6.

It will be appreciated, as explained hereinabove with respect to FIG. 6,that in an SBSMAP such as that defined by table 905 in FIG. 16, in whichonly the group type of the last group in a sequence of groups in anSBSMAP may determine the group scheduling protocol for the remainder ofthe TXOP to which that sequence of groups is assigned, the group typesvalues assigned to each row in the SBSMAP table may serve as separatorsto delineate the groups in the sequence, and they may not dictatescheduling protocol in the SBSMAP, except in the final group in thesequence.

Thus, in the example shown in FIG. 16, the alternating group type valuesof “5” and “6” assigned to the sub-burst slots in groups j, k and lserve to identify the sub-burst slots affiliated with each group, andnot group scheduling protocol. I.e., the first three sub-burst slots inthe table, which are assigned one group type value, are affiliated withone group, here referred to as group j, the next four sub-burst slots,which are assigned a different group type value, are affiliated withanother group, here referred to as group k, etc. In accordance with thisembodiment of the present invention, only the group type of the lastgroup, group m, may dictate group scheduling protocol in the sharedTXOP.

In systems which support advanced quality of service, each networkservice may conduct negotiations with the scheduler regarding mediaaccess parameters such as bandwidth, latency and jitter. For its part,the scheduler may agree to service requests for guaranteed levels ofservice in accordance with its abilities to meet the service demands.The ability of the scheduler to meet service requests may be dependentupon the demands on the network at the time of the requests. Networkservices may request that the scheduler provide them with minimum,average, maximum or best effort levels of guaranteed bandwidth.

Service requests for a minimum level of guaranteed bandwidth may be thebandwidth requirement requests given the highest priority for schedulingby scheduler 112 (FIG. 3), since a minimum level request by a networkservice may indicate that the service requires at least this level ofbandwidth in order to execute its transmissions. I.e., if the service isnot provided this minimum bandwidth, it will not be able to execute itstransmissions. Service requests for an average level of guaranteedbandwidth may be the bandwidth requirement given the next highestpriority for scheduling by the scheduler, followed by service requestsfor a maximum level of guaranteed bandwidth, followed by servicerequests for a best effort level of guaranteed bandwidth.

In accordance with the bandwidth allocation hierarchy describedhereinabove, the first group in a TXOP scheduled according to theadvanced quality of service scheme provided by the present invention maycomprise sub-burst slots for the services requesting a minimum level ofguaranteed bandwidth, i.e. the highest quality of service. Similarly,the second group in the TXOP may comprise sub-burst slots for theservices requesting an average level of guaranteed bandwidth, i.e. thenext highest quality of service, the third group in the TXOP maycomprise sub-burst slots for the services requesting a maximum level ofguaranteed bandwidth, i.e. the third highest quality of service, and thelast group in the TXOP may comprise sub-burst slots for the servicesrequesting a best effort level of guaranteed bandwidth, i.e. the lowestquality of service. It may therefore be seen in FIG. 16 that each of theservices associated with each of the sub-burst slots in group jrequested and received from the scheduler a transmission opportunityguaranteeing a minimum bandwidth level. It may further be seen in FIG.16, that due to the availability of 60 Mbps to the group of threesub-burst slots in group j, the bandwidth guaranteed to each service ineach of the group j sub-burst slots is 20 Mbps.

It may further be seen in FIG. 16 how Next_Group opportunities may beused in the advanced quality of service scheme provided by the presentinvention to guarantee different levels of bandwidth to networkservices. In a scheme similar to that described with respect to FIG. 15for the guaranteed bandwidth scheme provided by the present invention,Next_Group opportunities may be used in the advanced quality of servicescheme provided by an alternative embodiment of the present invention totransfer a guaranteed amount of bandwidth from one group, in which eachsub-burst slot represents a guaranteed amount of bandwidth, to the nextgroup. Each sub-burst slot in the beneficiary next group willconsequently be guaranteed a fraction of the transferred bandwidth. Thisfraction may equal the amount of transferred bandwidth divided by thenumber of sub-burst slots in the next group.

For example, as shown in FIG. 16, the division of the available 60 Mbpsamongst the three sub-burst slots in group j provides the highestpriority guaranteed minimum bandwidth of 20 Mbps to each sub-burst slotin group j, one of which is Next_Group opportunity 918. In the exampleshown in FIG. 16, Next_Group opportunities may be identified by theirassigned Device_ID and Flow_ID values of 63 and 0 respectively. They areindicated in table 905 by diagonal hatching and the reference numerals918, 920, 922 and 924. In the example shown in FIG. 16. Next₁₃Groupopportunity 918 transfers at least this 20 Mbps, and at most, all of thebandwidth not utilized in group j, to group k. In the example shown inFIG. 16, it may be seen that each of the network services associatedwith each of the sub-burst slots in group k, the second group in theSBSMAP, requested and received from scheduler 112 a transmissionopportunity guaranteeing an average bandwidth level. In the exampleshown in FIG. 16, it may be seen that the guaranteed average bandwidthlevel is 5 Mbps, which equals the 20 Mbps transferred to group k bygroup j divided among the four sub-burst slots in group k.

It may similarly be seen that the guaranteed maximum bandwidth level inthe example shown in FIG. 16, for the third group l in the SBSMAP, is2.5 Mbps, which equals the 10 Mbps transferred to group l by Next_Groupopportunities 920 and 922 in group k divided among the four sub-burstslots in group l.

It will be appreciated that the advanced quality of service schemeprovided by the present invention and illustrated with respect to FIG.16, may provide a method according to which scheduler 112 (FIG. 3) mayguarantee different levels of bandwidth to network services inaccordance with their requests, subject to the limitations of thenetwork at any given time. Furthermore, through the implementation ofNext_Group opportunities as described with respect to FIG. 16, highlyefficient use of available bandwidth may be achieved through theforwarding of any and all bandwidth remaining unused in one group to thesubsequent group. Thus, little or no bandwidth which a networkparticipant may be prepared to use may be wasted.

The generally efficient usage of bandwidth in the present invention maybe further enhanced by the periodic usage of a minimal MAP. A minimalMAP may be introduced into the transmission cycle during a Next Mapopportunity sub-burst slot which may be included in an SBSMAPconstructed and operative in accordance with an additional preferredembodiment of the present invention.

While a long transmission cycle may provide certain advantages withrespect to efficient bandwidth usage, such as minimizing the usage ofbandwidth for MAP advertisements over the network, the disadvantage of along, uninterrupted transmission cycle may be its rigidity. While thenetwork is committed to a particular media access plan, it is unable toreact to emergent situations on the network.

For example, time and bandwidth may be wasted while network servicesnegotiate with scheduler 112 (FIG. 3) for guaranteed bandwidth, asdescribed hereinabove with respect to FIG. 16. Next_MAP opportunitysub-burst slots scheduled in an SBSMAP provided by the present inventionmay constitute windows of opportunity for the scheduler to quicklyinterrupt the current MAP and transition to the next MAP. This featuremay allow usage of time and therefore bandwidth, which would haveotherwise been wasted while the original MAP ran its course.

The implementation of a Next_MAP opportunity in accordance with anadditional preferred embodiment of the present invention is describedwith respect to FIGS. 17A and 17B, reference to which is now made. Inexemplary timing diagram 950 for an exemplary SBSMAP shown in FIG. 17A,it may be seen that groups j and k, having three and four sub-burstslots each respectively, are scheduled through the duration of TXOP 955.Group j includes a Next_Group opportunity sub-burst slot, indicated bythe letter “N” and hatched, and group k includes a Next_MAP opportunitysub-burst slot, indicated by the symbol “M” and circled. It may be seenin FIG. 17A that during Next Group opportunity 960, group j passes thetransmission opportunity to the first participant in the queue in thenext group, which is the participant associated with sub-burst slot “0”in group k, as indicated by arrow 965. As can be seen in FIG. 17A, notransmission occurs during this sub-burst slot.

During Next_MAP opportunity sub-burst slot 962, scheduler 112 may havethe opportunity to interrupt the current TXOP 955, and begin a new TXOPwith the first group scheduled in the next MAP. It may be seen in FIG.17A that scheduler 112 passes on Next_MAP opportunity 962 to interruptthe TXOP and transmit the next MAP. Similarly, during Next_MAPopportunity 964, which occurs as a transmission opportunity istransferred from group j to group k during a Next_Group opportunity asindicated by arrow 966, scheduler 112 again does not act on theopportunity.

Reference is now made to FIG. 17B which shows an additional exemplarytiming diagram 950′ for an exemplary transmission cycle of the sameSBSMAP as that for which timing diagram 950 is shown in FIG. 17A. It maybe seen in timing diagram 950′ that scheduler 112 again passes on thefirst Next_MAP opportunity 962 in TXOP T0, but does act upon the secondNext_MAP opportunity 964. Consequently, as may be seen in FIG. 17B, TXOPT0 is interrupted at this point, as indicated by reference numeral 968,where scheduler 112 begins the transmission of the next MAP.Accordingly, after the IFG following this transmission, TXOP T1 isinitiated, as indicated by reference numeral 969.

Reference is now made to FIG. 18 which shows an additional preferredembodiment of the present invention implemented within a multi-dwellingunit (MDU) or a multi-tenant unit (MTU). In a prior art MxU, which maybe an MDU or an MTU, the master device is able to communicate with allof the endpoints (EPs) in the units owing to carrier sensing operatingbetween the master device and each of the EPs. In an MxU, each unit mayhave one or more EPs. In the prior art, each device, i.e., the masterand each EP, has a separate TXOP in order to guarantee media access.Media access is thereby guaranteed to the master for advertising mediaaccess plans over the network, and to the EPs, for data transmissions.

Multiple separate TXOPs in the prior art, required in an MxU for thelarge number of units if there is only one EP per unit, and for an evenlarger number of EPs if there is more than one EP per unit, result in aninefficient network having a large overhead and considerable bandwidthwastage.

As shown in FIG. 18, the present invention may provide a generally moreefficient method for utilizing available bandwidth in an MxU. As shownin timing diagram 980, which is an exemplary timing diagram for anexemplary transmission cycle for an SBSMAP constructed in accordancewith a preferred embodiment of the present invention and operative in anMxU in which there is carrier sensing between the master and all of theEPs, all of the network devices may participate in a single shared TXOPT0.

In an MxU in which there is carrier sensing between the master and allof the EPs, but not between all of the EPs amongst themselves, the EPsbetween which there is carrier sensing may participate in a shared TXOPin accordance with a preferred embodiment of the present invention. Asshown in timing diagram 982, each of shared TXOPs T1, T2 and T3 mayserve a group of EPs between which there is carrier sensing.

Shared TXOPs having sub-burst slots may also be implemented in a networkrunning a TCP protocol, resulting in more efficient bandwidth usage withrespect to the prior art, as shown in FIGS. 19A and 19B, reference towhich is now made. The TCP protocol is a bi-directional protocol inwhich data transmissions (TCP DATA) are followed by transmissionacknowledgements (TCP ACK) as shown in timing diagram 990. Eachdirection has its own dedicated TXOP, as indicated in diagrams 991 and992 showing TCP data transmissions by network device DEV-1 and TCPacknowledgements by network device DEV-2 respectively. To improveefficiency, there may be a buffer in which multiple data packets arestored until their transmission is acknowledged. The data packets may bestored until acknowledgement is received in case the transmission is notacknowledged and the packets must be sent again. As shown in FIG. 19A, anetwork running a TCP protocol may suffer from low effective throughput,due to the limitation of the buffer, as represented by TCP window 991.As a result of the limited TCP window 991, bandwidth portions WD1 andWD2 may be wasted, resulting in a long round-trip time (RTT). It mayfurther be seen in FIG. 19A that the minimal TCP ACK trafficunderutilizes the bandwidth allocated for the ACK stream resulting inadditional wasted bandwidth portions WA1 and WA2. In view of the amountof wasted bandwidth, as shown in FIG. 19A, it may be seen that theavailable bandwidth is inefficiently utilized.

As shown in FIG. 19B, the implementation of shared TXOPs 995 havingsub-burst slots in a network running a TCP protocol in an additionalpreferred embodiment of the present invention may provide a generallymore efficient method for utilizing available bandwidth with respect tothe prior art. As shown in FIG. 19B, one device Dev-1 may be associatedwith sub-burst slots numbered “1” in the SBSMAP, and may use thesesub-burst slots for TCP data transmission. For the acknowledgmenttraffic, a second device, Dev-2 may utilize the sub-burst slots numbered“2” in the SBSMAP. As may be seen in FIG. 19B, through theimplementation of sub-burst slot transmission opportunities, the TCPdata transmissions may occupy the transmission medium for the exactamounts of time required, as indicated I timing diagram 997 bytransmission durations LD1, LD2 and LD3, with no wastage of bandwidth.Similarly, as indicated by acknowledgement durations LA1, LA2 and LA3,the TCP acknowledgement transmissions may occupy the transmission mediumfor the exact amounts of time required, with no wastage of bandwidth. Itmay thus be seen that in accordance with the present invention TCP dataand acknowledge transmissions may occupy TXOP opportunities in a sharedTXOP as needed in a very efficient manner. The total RTT may also beminimal, and may be the real RTT of the devices and not the sharedmedia.

It will be appreciated that SBSMAPs constructed and operative inaccordance with a preferred embodiment of the present invention mayinclude any number of TXOPs, any number of which may contain sub-burstslots. The sub-burst slots may be grouped, according to a variety ofparameters such as data flow priority, device priority or quality ofservice (QoS) requirements. The sub-burst slots within a group may besequenced according to any algorithm, and the groups within a TXOP maybe sequenced according to any algorithm.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

What is claimed is:
 1. A network device forming part of a data network,said device comprising: a receiver to receive a MAP (Media Access Plan)which comprises a schedule with a plurality of initiation slots eachallocated to one of a plurality of network devices, wherein each saidinitiation slot has a length of less than a minimum burst duration ofany data transmission in said data network; a transmitter to initiate adata transmission during one of said plurality of initiation slotsassociated with said network device and to continue said datatransmission beyond an end of the one of said plurality of initiationslots until said data transmission is complete; and a grid aligner tostop said schedule at a current initiation slot when a data transmissionbegins from the network device allocated to said current initiation slotand to recalculate the timing of said schedule due to the duration ofsaid data transmission at the next initiation slot following the currentinitiation slot according to an original temporal order of initiationslots in said schedule to allow for a transmission from the networkdevice allocated to said next initiation slot.
 2. The method accordingto claim 1 and comprising scheduling said plurality of initiation slotswithin at least one shared transmission opportunity (TXOP).
 3. Themethod according to claim 2 and wherein said schedule starts at abeginning of said at least one shared TXOP.
 4. The method according toclaim 1 and wherein said minimum burst duration is sufficient totransmit at least a single data frame.
 5. The method according to claim4 and wherein a length for said minimum burst duration is variable. 6.The method according to claim 1 and and wherein said plurality ofinitiation slots are organized into modular groups.
 7. The methodaccording to claim 6 and wherein each of said modular groups isassociated with one of a plurality of group types.
 8. The methodaccording to claim 6 and wherein an initial modular group sequencecomprises at least one of a single modular group and a sequence of saidmodular groups.
 9. The method according to claim 8 and wherein a grouptype of a last scheduled group in initial modular group sequencedetermines a subsequent sequence of scheduled groups following saidinitial modular group sequence.
 10. The method according to claim 1 andwherein different quantities of said plurality of initiation slots areallotted to said network participants.
 11. The method according to claim10 and wherein said different quantities are proportionate to bandwidthrequests of said network participants.
 12. The method according to claim6 and wherein an explicit group separator is scheduled in at least oneof said modular groups having a particular number of initiation slots todefine a quantity of said initiation slots to be scheduled for said atleast one said modular group wherein said quantity is different thansaid number.
 13. The method according to claim 6 and in at least one ofsaid modular groups, at least one next group opportunity initiation slotis scheduled for a succeeding modular group.
 14. The method according toclaim 6 and an amount of bandwidth is divided equally among initiationslots of a modular group.
 15. The method according to claim 13 and anamount of bandwidth is divided equally among said plurality ofinitiation slots of a said modular group wherein at least one of saidinitiation slots is one of said at least one next group opportunityinitiation slots.
 16. The method according to claim 6 and wherein in atleast one of said groups, a next map opportunity initiation slot isscheduled for interrupting said schedule.
 17. The method according toclaim 1 and wherein said network device is a HPNA network device. 18.The method according to claim 1 and wherein said data transmission isinitiated at a beginning of said initiation slot.
 19. The methodaccording to claim 18 and wherein said beginning is within the first 2-4μsecs of said time slot.
 20. The method according to claim 7 and whereineach of said group types is at least one of the following types: fixed,rotated, and repeated.
 21. The method according to claim 7 and whereineach one of said group types is associated with a post-transmissionscheduling protocol dictating which initiation slot is scheduled after atransmission.
 22. The method according to claim 7 and wherein each oneof said group types is associated with a group scheduling protocoldictating a scheduled sequence of groups.
 23. The method according toclaim 22 and wherein a duration of time allotted to said scheduledsequence of groups is longer than a sum of durations of initiation slotsin said modular groups.
 24. The method according to claim 22 andcomprising indicating parameters for an entry of said MAP, wherein theparameters include: a device identification number identifying a networkparticipants; a group type number associated with one of said pluralityof group types; a data flow identification number associated with a dataflow; a TXOP_number assigned to sequential transmission opportunity(TXOP); and a TXOP length dictating a length of a TXOP.
 25. The methodaccording to claim 7 and wherein at least one of said plurality ofinitiation slots is a registration time slot.
 26. The method accordingto claim 6 and wherein each of said modular groups is associated with apriority level.
 27. The method according to claim 6 and wherein for atleast one of said modular groups having a particular number ofinitiation slots, a different number of said initiation slots isscheduled for at least one group.
 28. A method for a data network, themethod comprising: receiving a MAP (Media Access Plan) which comprises aschedule with a plurality of initiation slots each associated with oneof a plurality of network devices, wherein each said initiation slot hasa length of less than a minimum burst duration of a data transmission insaid data network; and following said MAP, wherein said followingcomprises: listening for data transmissions associated with saidplurality of initiation slots; detecting a data transmission from thenetwork device allocated to a current initiation slot, said datatransmission extending beyond an end of said current initiation slot;stopping said schedule at said current initiation slot when said datatransmission is detected; and recalculating the timing of said scheduledue to the duration of said data transmission at the next initiationslot following the current initiation slot according to an originaltemporal order of initiation slots in said schedule to allow for atransmission from the network device allocated to said next initiationslot.